Lock plate arrangement

ABSTRACT

In gas turbine engines it is found that leaked coolant flow through the lock plates  28, 29, 50, 60  can be used to insulate the rotor surfaces  33, 34  from the effects of hot gas ingestion. In order to enhance this effect chutes  39, 59, 69  are provided to guide the leakage airflow adjacent to the lock plate such that the ingested hot gas flow is prevented from coming into contact with the surfaces of the lock plate and other cavity surfaces  33, 34  to improve cooling effect. The chutes  39, 59, 69  create apertures  40, 53  which can be of dimensions to ensure that there is a high ratio between width and depth of the coolant flow  32  again facilitating heat exchange and cooling efficiency.

The present invention relates to turbine engine cooling and moreparticularly to cooling with respect to the hot turbine stages of a gasturbine engine about the turbine blade mountings between turbine stages.

Referring to FIG. 1, a gas turbine engine is generally indicated at 10and comprises, in axial flow series, an air intake 11, a propulsive fan12, an intermediate pressure compressor 13, a high pressure compressor14, combustion equipment 15, a high pressure turbine 16, an intermediatepressure turbine 17, a low pressure turbine 18 and an exhaust nozzle 19.

The gas turbine engine 10 works in a conventional manner so that airentering the intake 11 is accelerated by the fan 12 which produce twoair flows: a first air flow into the intermediate pressure compressor 13and a second air flow which provides propulsive thrust. The intermediatepressure compressor compresses the air flow directed into it beforedelivering that air to the high pressure compressor 14 where furthercompression takes place.

The compressed air exhausted from the high pressure compressor 14 isdirected into the combustion equipment 15 where it is mixed with fueland the mixture combusted. The resultant hot combustion products thenexpand through, and thereby drive, the high, intermediate and lowpressure turbines 16, 17 and 18 before being exhausted through thenozzle 19 to provide additional propulsive thrust. The high,intermediate and low pressure turbine 16, 17 and 18 respectively drivethe high and intermediate pressure compressors 14 and 13, and the fan 12by suitable interconnecting shafts.

It will be appreciated from above that the turbine blades requireappropriate mounting in order to allow rotation for operationalperformance in creating a propulsive axial gas flow, but also that theblades must be appropriately cooled. It will be understood that turbineengine efficiency is closely related to operational temperatures andthat acceptable operational temperatures are dictated to a significantextent by the material properties of the components. In suchcircumstances by appropriate cooling it is possible to operate thesecomponents near to and occasionally exceeding the melting points for thematerials for which they are constructed.

In order to provide cooling, generally coolant air is taken from thecompressor stages of a gas turbine engine. Thus, this drainage ofcompressed coolant air reduces engine efficiency. It is an objective toutilise coolant air flows as effectively as possible in order tominimise the necessary coolant flow to achieve a desired level ofcomponent cooling for operational performance. In such circumstancesgenerally there are relatively intricate coolant passageways providedwithin the engine components which are arranged to provide cooling asthe coolant passes through these passages as well as provide generallynozzle projection of the coolant flows where required into cavities inorder to create turbulence with hot gas flows for a cooling dilutedeffect.

FIG. 2 illustrates a schematic cross-section of a prior coolingarrangement as a schematic cross-section. Thus a blade root 1 forms ashank with a locking plate 2 presented across the root 3 of the blade.With a gas turbine engine, banks of turbine blades are provided and itis necessary to provide sealing between each turbine stage of theengine. Thus, seals 4 are provided in the form of a labyrinth sealarrangement with coolant airflow in the direction of arrowhead 5presented upwardly into the cavity 6 formed between the mounting disc 7for the blade 1 and the bottom of a nozzle vane defining the turbinestages. As can be seen there is a gap 8 through which hot gas isingested to the cavity 6. It is found that cooling air leakage flow 9generally creates a barrier layer around the surfaces of the cavity 6particularly on the rotor surface. Previously, the coolant air 5 hasbeen arranged to prevent excessive hot gas ingestion 8.

The lock plate acts to secure location of the blade shank such thatcoolant flow is contained or at least restricted below the blade shank.It will be appreciated that as described in U.S. Pat. No. 6,290,464, anarea 10 adjacent the lock plate is typically of what is known as a firtree root nature and designed to allow coolant air to flow across it atits surface and possibly through passages (not shown) in the fir treeroot in order to provide cooling. As turbine engines rotate about acentral shaft they are inherently circumferential and it is thereforenecessary that the lock plate is segmented. In such circumstances thegaps between the lock plates allow coolant leakage into the cavity. U.S.Pat. No. 629,464 describes provision of an outlet nozzle in order toproject coolant flow through the fir tree root coolant passages intosuch a cavity in order to create turbulence and therefore cooling withinthat cavity. Such an approach does not utilise the boundary layercreated by the lock plate leakage to protect the disc rim from ingestionof hot gas through the gap.

In accordance with the present invention there is provided a lock platefor a blade mounting assembly within a gas turbine engine, the lockplate integrally shaped to form a chute for direct outward marginal flowacross the lock plate for presentation of a coolant flow substantiallyin alignment with the lock plate.

Typically, the chute is formed in an end of the lock plate.Alternatively, the chute is formed intermediately between ends of thelock plate. Alternatively, the chute is formed by a passage shapedwithin the width of the lock plate.

Generally, the chute extends substantially across the width of the lockplate. Possibly, the chute varies in dimensions dependent upontemperature.

Normally, the lock plate is formed by casting or moulding or machining.

Possibly, the lock plate incorporates spacer protrusions upon at leastone end in order to provide regulation of spacing between adjacent lockplates in use.

Also in accordance with the present invention there is provided a platemounting arrangement for a gas turbine engine, the arrangementcomprising a lock plate associated with a mounting disc for a pluralityof turbine blades, the lock plate defined as above.

Normally, a plurality of lock plates are provided in alignment about amounting disc to form a circumferential barrier.

Generally, the chute is configured to co-operate with an overflow inorder to retain the coolant flow adjacent to the lock plate.

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings in which;

FIG. 3 is a schematic perspective view of a blade mounting incorporatinga lock plate arrangement in accordance with the present invention;

FIG. 4 is a schematic perspective view illustrating adjacent lock platesin accordance with the present invention;

FIG. 5 is a front perspective view in the direction X of a lock plate asdepicted in FIG. 3;

FIG. 6 is a schematic plan view of the lock plate arrangement depictedin FIG. 3 in the direction of arrowhead Y;

FIG. 7 is a schematic front perspective of an alternative lock plate inaccordance with the present invention;

FIG. 8 is a front perspective view of the lock plate depicted in FIG. 6in the direction of arrowhead Z;

FIG. 9 is a schematic cross-section in the direction of A-A of a lockplate depicted in FIGS. 6 and 7; and

FIG. 10 is a schematic front perspective view of a further refinement ofa lock plate in accordance with the present invention.

Those knowledgeable with respect to lock plates utilised within gasturbine engines will understand that it is not possible to provide acomplete barrier seal between lock plates. A number of lock plates arerequired in order to create the circumferential barrier seal around amounting disc for turbine blades and the junctions of these plates willlead to varying degrees of coolant air leakage.

Recent behavioural studies have indicated that cooling air emerging fromlock plate type gaps into a turbine stator cavity 6 (FIG. 2) in thepresence of a net gas ingestion at the rear of a turbine mounting dischas beneficial effects with respect to cooling. Net gas ingestion occurswhen the flow requirement of an inter-stage labyrinth seal exceeds thesupply of cooling air to the upstream stator well, that is to sayresulting in a supplementary flow drawn from the turbine main annulargas flow drawn through the gap between the rotor and stator platforms.

Observation of this cooling air and gas ingestion has shown that theleakage air from the lock plate is retained within a disc rim boundarylayer having a disproportionately beneficial effect on disc rim coolingwhen hot air ingestion is also present. Thus, there is a relativelyenhanced effective cooling of the rotor by a relatively small coolantair supply provided by that lock plate to lock plate end gap leakage.Unfortunately, this leakage as indicated previously is variable withprior arrangements. Nevertheless, by providing more regulation withrespect to this leakage it will be possible to provide significantsavings in cooling air supply compared with more traditional approaches.

The process by which the coolant air acts is as a result of jets ofhigher pressure cooling air emerging from the lock plate between thelock plate end faces into the stator well cavity at the rear of a discrim. This coolant air is held within the boundary layer travellingradially inwards towards the labyrinth seal rather than penetratingthrough the boundary layer. Clearly, coolant air retained adjacent tothe cavity wall surfaces will have an enhanced effect with respect tocooling. It will also be understood that this effect increases therelative amount of coolant air and reduces the amount of annulus gas inthe boundary layer significantly again maintaining relatively low localtemperatures. For information and as indicated above, it was previouslyconsidered necessary to assume a thorough mixing of the ingested hotannulus gas and the cooling air for cooling effectiveness.

It will be understood that hot gas ingestion occurs whenever the coolingflow supplied to the rim gap is less than the critical value required toseal the rim gap. In the case of an inter-stage seal cavity where thelabyrinth seal clearance is such that the cooling flow is drawn off tothe lower pressure “sink”, downstream of the stage nozzle guide vane,leaving the gap at the rear of the upstream rotor short of the necessaryflow requirements to create the seal at the annulus. Thus, as enginescomplete more and more service cycles and the inter-stage seals tend towear there is also an increase in the clearances and redistributing thenormally fixed level of coolant flow towards the rear stator well. Thisincreases the risk of hot gas ingestion in the front of the well.

It will be understood that cooling is a safety as well as operationalpriority so there is a requirement to ensure that there is alwayssufficient cooling air supply even when worst wear clearances areexperienced. There is a balance between the cooling supply and hot gasingestion dependent upon many factors including the static pressure inthe gas turbine annulus, the losses in the cooling air feed system, anyflow dependent on a vortex, rotating hole, clearance diameters or sealclearance subject to a combination of rotor speeds, the main annuluspressure ratios and transient effects such as seal clearances. In suchcircumstances, a range of conditions over which hot gas ingestion mayoccur and the level of ingestion will certainly vary. However, sinceentrainment flow is speed dependent, engines are normally mostvulnerable at maximum shaft speeds.

Prior sealing systems deliver the bulk of the rim sealing air flow viaradial holes in a disc drive arm. In addition to not making best use ofthe air flow cooling the disc rim, considerable work is put into the airto accelerate it to the speed of the rotor. This has a negative effectupon turbine efficiency. Thus, as the present invention utilises lesscooling air it will be appreciated that less cooling air will requireacceleration to the rotor speeds. Additionally, a significant proportionof the work done in accelerating the air to the speed of the rotor isrecovered by directing the cooling air against the direction ofrotation.

As indicated above it is necessary to regulate and meter the leakageflow between the lock plates in order to take full advantage of theboundary layer cooling effects. Thus, spacer protrusions are used inaccordance with the present invention in order to regulate the gapbetween the ends of the lock plates. In such circumstances, there is acoolant leakage flow through the gaps between the lock plates and asdescribed previously this is retained adjacent to the cavity wall evenin the presence of the hot gas ingestion effect described above. It willbe appreciated that chutes may also be provided in order to furtherenhance this leakage coolant air flow adjacent to the cavity wall.

Referring to FIG. 3 and as indicated above, the ingested hot gas drawnabout the aligned lock plates 28, 29 is known to retain a leaked coolantflow 32 adjacent to the lock plates 28, 29. In such circumstances,utilisation of the coolant flow 32 should be optimised. In order toachieve this chutes 39 are provided. These chutes 39 act to direct theleakage flow 32 effectively adjacent to the lock plates 28, 29 both interms of release of that flow 32 as well as protecting the rotorsurfaces 33, 34 from the hot gas ingestion 35. By having the coolantflow adjacent to the wall surfaces of the lock plates 28, 29 as well aswalls 33, 34 of the cavity 38 it will be understood that greater coolingeffects with respect to the components forming these walls is achieved.

In contradiction to previously understood processes avoidance ofturbulence is required in order to maintain the flow 32 adjacent to thelock plates 28, 29 as well as the wall surfaces 33, 34. Thus, the chutes39 are arranged to have an aperture 40 which extends over a substantialproportion of the width of the lock plates 28, 29 such that there islimited jetting which may create turbulence. Furthermore, these chutes39 are shown in the form of an incline or ramp created in the lockplates 28, 29 to allow the cooling airflow 23 to be introduced into thestator well cavity 38 in the most beneficial direction and for smoothdeflection of hot gas flow 35 away from the rotor surfaces 33, 34. Thelock plates 28, 29 will generally be formed by a casting or moulding ormachining process in order to create the necessary chute for flow 32 tobe retained within the disc boundary layer.

As depicted in FIG. 3 generally the chutes 39 will be formed towards arear end of the lock plates 28, 29 that is to say downstream of therotation direction 25 for the arrangement. However, as will be describedlater, chutes may be formed between the ends of the lock plates asrequired by operational performance.

Referring to FIGS. 4 to 6 illustrating a lock plate arrangement inaccordance with the present invention. Thus, a lock plate 50 isassociated with a lock plate 51 such that respective ends abut eachother at a joint 52. As indicated previously this joint is not perfectand therefore in use will tend to leak a coolant flow as described inFIG. 1 by reference to arrowheads 32. Chutes 59 are provided at the endsof the lock plates 50, 51 generally downstream of the direction ofrotation (arrowhead 55). The chutes 59 are formed such that a rampeffect is created to divert the ingested hot flow as describedpreviously and provide an opening or aperture 53 for presentation of thecoolant airflow 32 (FIG. 3). The chutes 59 are integral with the lockplates 50, 51 and as indicated above are generally formed during amoulding or casting process.

FIG. 5 illustrates the downstream end of the lock plate 50 in thedirection X (FIG. 4). Thus, the aperture 53 creates a flow passage forthe coolant flow 32 (FIG. 3) by outwards projection from an adjacentlock plate illustrated by broken line 54. In such circumstances, ifcoolant flow is projected out of the aperture 53 adjacent to that lockplate 54 and as described previously the effect of the ingested hot gasflow 35 (FIG. 2) is to retain that flow adjacent to the lock plate 51and other surfaces downstream.

It will be noted that the aperture 53 extends through a substantialproportion of the width of the lock plate 50 to again maximise the widthof the coolant flow 32 (FIG. 3) in comparison with the depth, that is tosay the extent by which the flow 32 extends from adjacent to the surfaceof the lock plate 34. It will be understood that a thin coolant flow 52relative to depth will substantially increase the “contact surface”between that flow 32 and the disc surfaces 33, 34 increasing coolingefficiency. Such spreading of the flow can be considered to create amarginal cooling flow layer adjacent to the component surfaces to becooled.

FIG. 6 provides a schematic plan view of the junction 52 between lockplates 50 and 51. Thus, the chute 59 extends outwardly along theaperture 53 through which the coolant air flow 132 passes. It will benoted that this flow 132 remains relatively close to a wall surface 56for cooling efficiency. As described previously, ingested hot gas flow135 passes over the chute 59 and constrains the flow 132 as a barrierlayer adjacent to the surface 56 again to facilitate cooling efficiency.

The actual dimensions of the chute 59 will be determined byconsiderations as to the desired presentation of the flow 132 and thepotential flow disturbing effects of the chute 59 upon the overlayingingested flow 135. Nevertheless, as described above, generally the chute59 will extend across a substantial proportion of the width of the lockplates to ensure a high width to depth ratio for the flow 132 maximisinginsulation effectiveness.

As indicated above there is a general leakage about the junction betweenlock plates and observation has noted that this leakage is retained in aboundary layer adjacent to the lock plate. Thus, FIGS. 7 to 9 illustratean alternative embodiment of the present invention in which a chute 69is formed within the width of a lock plate 60. In effect this chute 69is a specifically shaped and formed slot formed in the lock plate 60such that there is no surface protrusion whilst the chute 69 turns acoolant flow 232 for entrainment insulating the rotor surfaces 33, 34from an ingested hot gas flow 235 as described previously. The chute 69is shaped to meter and regulate the coolant flow 232 such that this flowexpands efficiently using the pressure drop across the lock plate 60. Insuch circumstances the hot gas ingestion flow 235 is kept away from thedisc surfaces 33, 34 with the coolant flow 232 forming a barrier flowingadjacent to a surface 66 of the lock plate 60 for best cooling effect.As previously the chute 69 extends substantially across the width W-W ofthe lock plate 60 to increase the potential barrier to hot gas ingestionon the rotor surfaces.

Most conveniently the slot 69 is forwarded by casting the lock plate 60and then finalising the shape of that chute 69 through machiningprocesses. Dependent upon requirements more than one intermediate chutecan be provided in a lock plate in accordance with the presentinvention. Care must be taken with respect to the pressure differentialutilised in order to generate coolant flow.

As indicated above it is provision of a relatively smooth coolant flowwhich can remain attached to surfaces for insulating effect under theblanketing flow of the ingested hot gas which provides the particularbenefit and improving overall cooling efficiency relative to the volumeof coolant used. In such circumstances spaces and protrusions can beutilised in order that the gap between the lock plates is regulated suchthat the coolant that flows through the gap is consistent and thereforecan reduce the effects of the ingested hot gas flows. FIG. 10illustrates several lock plates 90 between which spacer protrusions 91act to regulate the gap 92 between the ends of the lock plates 90. Insuch circumstances a regulated gap 92 is provided through which theleakage coolant flow can be presented to the rotor surface 33 and 34FIG. 3 and through use of the spaces 91 this gap 92 can be consistentthroughout the circumferential barrier created by the lock plates 90 ofa gas turbine engine. Intermediate chutes 93 can be provided in order torefresh the coolant flow at intermediate positions between the ends ofthe lock plates 90 again with consistent cooling effect and efficiency.

It will be understood that the spacer protrusions 91 generally take theform of pips which prevent chocking and provide a controlled minimum gap92. This gap 92 allows cooling air into the stator wall cavities etc.for cooling purposes as described previously adjacent to walls withthose cavities.

As can be seen in FIG. 3 spacer protrusions 31 can also be provided withrespect to chutes formed at the ends of lock plates 28, 29 in order toagain facilitate and regulate the coolant air flow 32 presented by thechutes 39. In these circumstances the spacer protrusions 31 aregenerally positioned towards the side edges of the ends of the lockplates 28, 29 to allow accommodation of the relatively broad chutes 39.

The spacer protrusions 31 may enter dimples in the opposed lock platesurface for location purposes.

Modifications and alterations to the embodiments of the presentinvention will be envisaged by those skilled in the art. Thus, withrespect to chutes 39, 59 it may be possible to create an overhang whichextends beyond the end of the lock plate in order to lay over a portionof the adjacent lock plate in order to further facilitate coolant flowpresentation for retention adjacent to the lock plate surface and otherwall surfaces of the turbine engine for cooling purposes.

1. A lock plate for a blade mounting assembly within a gas turbineengine, the lock plate characterised by being integrally shaped to forma chute for direct outward marginal flow across the lock plate forpresentation of a coolant flow substantially in alignment with the lockplate.
 2. A plate as claimed in claim 1 wherein the chute is formed inan end of the lock plate.
 3. A plate as claimed in claim 1 wherein thechute is formed intermediately between ends of the lock plate.
 4. Aplate as claimed in claim 1 wherein the chute is formed by a slot shapedwithin the width of the lock plate.
 5. A plate as claimed in claim 1wherein the chute extends substantially across the width of the lockplate.
 6. A plate as claimed in claim 1 wherein the chute varies indimensions dependent upon temperature.
 7. A plate as claimed in claim 1wherein the lock plate is formed by casting or moulding or machining. 8.A plate as claimed in claim 1 wherein the lock plate incorporates spacerprotrusions upon at least one end in order to provide regulation ofspacing between adjacent lock plates in use.
 9. A lock plate mountingarrangement for a gas turbine engine, the engine comprising a pluralityof blades secured by lock plates in a mounting whereby there is acoolant leakage flow in use and an ingested hot gas flow about theblades by the operational function of the blades, the arrangementcharacterised by the lock plates associated with the mounting for theplurality of turbine blades, being as claimed in any preceding claim,and the chute being arranged to present the coolant flow adjacent thelock plates for insulating the rotor surfaces from the effects of hotgas ingestion.
 10. An arrangement as claimed in claim 9 wherein theplurality of lock plates are provided in alignment about a mounting discto form a circumferential barrier.
 11. An arrangement as claimed inclaim 9 wherein the chute is configured to minimise the effect of theingressed hot gas flow by retaining the coolant flow adjacent to therotor surfaces.
 12. An arrangement as claimed in claim 9 wherein thechute extends over an edge of an adjacent lock plate.
 13. A gas turbineengine incorporating a lock plate as claimed in claim 1.